Pairing of Components in a Direct Current Distributed Power Generation System

ABSTRACT

A method of signaling between a photovoltaic module and an inverter module. The inverter module is connected to the photovoltaic module. In an initial mode of operation an initial code is modulated thereby producing an initial signal. The initial signal is transmitted from the inverter module to the photovoltaic module. The initial signal is received by the photovoltaic module. The operating mode is then changed to a normal mode of power conversion, and during the normal mode of operation a control signal is transmitted from the inverter to the photovoltaic module. A control code is demodulated and received from the control signal. The control code is compared with the initial code producing a comparison. The control command of the control signal is validated as a valid control command from the inverter module with the control command only acted upon when the comparison is a positive comparison.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of pending U.S. patentapplication Ser. No. 12/329,525 filed on Dec. 5, 2008 by the presentinventors the disclosure of which is included herein by reference. Thepresent application claims priority from pending U.S. patent applicationSer. No. 12/788,066 filed on May 26, 2010.

FIELD AND BACKGROUND 1. Field

The present invention relates to power generation systems, andspecifically to a system and method for reducing crosstalk whilesignaling between the components in direct current distributed powergeneration systems.

2. Related Art

A photovoltaic power generation system may incorporate one or morephotovoltaic panels with optional electronic modules attached thereto.An inverter connects to the photovoltaic panels or electronic modules.Power output from the photovoltaic panels or electronic modules isdirect current (DC) power. The electronic modules may perform directcurrent DC-to-DC conversion. The inverter inverts the DC power output toalternating current (AC) power.

As previously disclosed by the present inventors in US patentapplication publication 2008/0147335, the DC power cables connectinginverters to photovoltaic panels and/or electronic modules may provide acommunication channel between the inverters and the photovoltaic panelsor modules. The communication channel between inverters and modules,allows monitoring of the performance of the modules for monitoringtemperature, current, voltage and power output of a the photovoltaicmodules and potential allows for control of the modules.

Typically, lengths of cables connecting the inverter to the panels ormodules may be long and may contain one or several wire cores. Within aphotovoltaic installation, a wire at positive potential and a wire atnegative potential electrically associated therewith may be physicallyproximate thereto only at a point of connection to a piece of equipment.However, elsewhere in the photovoltaic field, the wires may be separatedand not be within the same cable run. The topography of the distributedpower generation system to a large extent dictates the installation andplacement of cable runs.

Physical proximity of wires not having an electrical association mayincrease the chances of the wires in the cables being subject to theeffects of noise if those wires are to be considered for signaling by DCpower line communications. Crosstalk is a type of noise which refers toany phenomenon by which a signal transmitted on a cable, circuit orchannel of a transmission system creates an undesired effect in anothercable, circuit or channel. Crosstalk is usually caused by undesiredcapacitive, inductive, or conductive coupling from one cable, circuit orchannel, to another. Crosstalk may also corrupt the data beingtransmitted. Typical known methods of preventing the undesirable effectsof crosstalk may be to utilize the shielding of cables, modules, panels,inverters or using twisted pair cables. Additionally, filteringtechniques such as matched filters, de-coupling capacitors or chokes maybe used to prevent the undesirable effects of crosstalk. However, thesetypical ways of preventing the undesirable effects of crosstalk aretypically unavailable or impractical for power line communications overDC lines in a power generation system and/or may be prohibitivelyexpensive in terms of additional materials and/or components required.

In a photovoltaic power generation system, with power line communicationover DC cables, it may be desirable to send a control signal between andan inverter and a particular photovoltaic module but no other modules.Crosstalk may cause the other photovoltaic modules in the powergeneration system to inadvertently receive the control signal which isof course undesirable.

Thus there is a need for and it would be advantageous to have a systemand method of reducing cross-talk in DC power line communications in adistributed DC power generation system, e.g photovoltaic DC powergeneration system.

The term “memory” as used herein refers to one or more of read onlymemory (PROM), erasable programmable read only memory (EPROM),electrically erasable programmable read only memory (EEPROM), FLASHmemory, optical memory, e.g. compact disk, switches, random accessmemory (RAM), magnetic memory such as a hard disk or other memory typesknown in the art.

The term “direct current (DC) power source” as used herein refers to(DC) power source such as batteries, DC motor generator; switch modepower supply (SMPS), photovoltaic panels and/or photovoltaic panelsoperatively attached to a converter module such as a DC to DC converter.

The term “photovoltaic source” as used herein refers to a photovoltaicpanel and/or a photovoltaic panel operatively attached to a electronicmodule which includes for instance a DC-to-DC converter. The term“electronic module” and “photovoltaic module” are used hereininterchangeably and refer to a functional electronic circuit attached toa photovoltaic panel.

The term “noise” as used herein in a communication channel, includes anyunwanted signal finding itself in the communication channel. Sources ofnoise may include radio frequency interference (RFI), mains electricityhum, unsuppressed switching voltages and crosstalk.

The term “crosstalk” as used herein refers to any phenomenon by which asignal transmitted on a cable, circuit or channel of a transmissionsystem creates an undesired effect in another cable, circuit or channel.Crosstalk is usually caused by undesired capacitive, inductive, orconductive coupling from one cable, a circuit, part of a circuit, orchannel, to another.

The term “telemetry” as used herein refers to measurement, transmissionand reception of data by wire, radio, or other means from remotesources. In the context of the present invention, telemetries are fromthe photovoltaic panels.

The term “transducer” as used herein refers to a device used for theconversion of one type of energy to another, for example, the devicechanges electrical energy in to electromagnetic energy and vice versa.The term “transducer” herein may also have functions of a sensor ordetector. The terms “sensor” and “transducer” as used herein are usedinterchangeably.

The terms “signal”, “signaling” or “signaling mechanism” as used hereinrefers to a signal modulated on a carrier signal. The carrier signal maybe an electrical or an electromagnetic signal. The signal may be asimple on/off signal or a complex signal which imparts information asdata. For a modulated signal, the modulation method may be by any suchmethod known in the art, by way of example, frequency modulation (FM)transmission, amplitude modulation (AM), FSK (frequency shift keying)modulation, PSK (phase shift keying) modulation, various QAM (quadratureamplitude modulation) constellations, or any other method of modulation.Although strictly, the terms “modulation” and “coding” are notequivalent, the term modulation and demodulation are typically usedherein to include coding and decoding respectively.

The term “signal strength” as used herein refers to the magnitude of theelectric field/current or voltage at a reference point that is asignificant distance from a transmitting source. Typically, “signalstrength” is expressed in voltage per length or signal power received bya reference point expressed in decibel (dB) per length (meter),dB-millivolts per meter (dBmV/m), and dB-microvolts per meter (dBμV/m)or in decibels above a reference level of one milliwatt (dBm).

The term “positive comparison” in reference to the comparison of twocodes or two signals means equal within tolerances or thresholds orderivable one from the other in a known way.

BRIEF SUMMARY

According to the present invention there is provided a method ofsignaling between a photovoltaic module and an inverter module. Theinverter module is connected to the photovoltaic module. In an initialmode of operation an initial code is modulated to produce an initialsignal. The initial signal is transmitted from the inverter module tothe photovoltaic module. The initial signal is received by thephotovoltaic module. The operating mode is then changed to a normal modeof power conversion, and during the normal mode of operation a controlsignal is transmitted from the inverter to the photovoltaic module. Acontrol code is demodulated and received from the control signal. Thecontrol code is compared with the initial code producing a comparison.The control command of the control signal is validated as a validcontrol command from the inverter module with the control command onlyacted upon when the comparison is a positive comparison. Current outputof photovoltaic modules may be limited during the initial mode ofoperation. The initial code is typically saved in a memory. Modulatingthe code may be performed by varying the input impedance of the invertermodule to produce a variation in voltage or current at the output of thephotovoltaic module. The photovoltaic module senses the variation involtage or current at the output of the photovoltaic module. Respectivesignal strengths for the initial signal and the control signal may bemeasured. The signal strengths are compared to produce a comparisonresult. When the comparison result is greater than a previously storedthreshold value then an alarm is set or the control command isinvalidated. Fluctuations prior to measuring the signal strength arepreferably filtered out. Electrical energy is typically stored forsupplying power for the varying and the sensing.

According to the present invention there is provided a photovoltaicgeneration system with a photovoltaic module including a firsttransceiver connected to the DC power line. A load module is connectedto the DC power line. The load module including a second transceiver isconnected to the DC power line. There is a pairing mechanism and asignaling mechanism between the first and second transceivers. Based onthe pairing mechanism, another photovoltaic module or another loadmodule in the photovoltaic generation system is excluded from signalingwith either the photovoltaic module or the load module. A charge storagedevice may be included within the photovoltaic module adapted to storecharge and supply power to the photovoltaic module. A secondphotovoltaic module may be attached to the photovoltaic module alongwith a second signaling mechanism adapted to signal between thephotovoltaic module and the second photovoltaic module. The signalingmechanism is typically configured to signal controls to the secondphotovoltaic module by relaying commands through the second signalmechanism. The signaling mechanism may also be configured to monitor thesecond photovoltaic module by receiving telemetries through the secondsignal mechanism. A transducer is optionally connected to the DC powerline and the first transceiver to modulate/demodulate a signal onto/fromsaid power line and a sensor may be connected to the DC power line andthe second transceiver to demodulate/modulate the signal from/onto saidpower line. In an initial mode of operation, an initial signal from theload module is transmitted to the photovoltaic module and an initialcode is demodulated by the photovoltaic module. In a subsequent normalmode of operation the initial code is used to validate a control commandfrom the load module. A memory may also be included within thephotovoltaic module, the memory preferably adapted to store the initialcode.

The foregoing and/or other aspects will become apparent from thefollowing detailed description when considered in conjunction with theaccompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1a shows a power generation circuit according to an embodiment ofthe present invention.

FIG. 1b shows further details of a transceiver attached to the output ofphotovoltaic modules in the power generation circuit shown in FIG. 1aaccording to an embodiment of the present invention.

FIGS. 1c and 1d illustrate respective methods of modulation anddemodulation according to aspects of the present invention.

FIG. 1e shows further details of a control and communications unitattached to the load shown in FIG. 1 a, according to features of thepresent invention.

FIG. 2 shows a method according to an embodiment of the presentinvention.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below to explain the presentinvention by referring to the figures.

It should be noted, that although the discussion herein relatesprimarily to methods in photovoltaic systems, the present invention may,by non-limiting example, alternatively be configured as well using otherdistributed power systems including (but not limited to) wind turbines,hydro-turbines, fuel cells, storage systems such as battery,super-conducting flywheel, and capacitors, and mechanical devicesincluding conventional and variable speed diesel engines, Stirlingengines, gas turbines, and micro-turbines.

It should be noted that although embodiments of the present inventionare described in terms of an inverter as a load, the present inventionmay be applied equally well to other loads including non-grid tiedapplications such as battery chargers and DC-DC power converters.

Before explaining embodiments of the invention in detail, it is to beunderstood that the invention is not limited in its application to thedetails of design and the arrangement of the components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments or of being practiced or carried out invarious ways. Also, it is to be understood that the phraseology andterminology employed herein is for the purpose of description and shouldnot be regarded as limiting.

The term “pairing or paired” as used herein refers to at least two powergeneration system components such as an inverter on one side, and on theother side photovoltaic panels and/or electronic modules which are“paired” or associated with each other.

“Pairing” establishes an association between an inverter and aparticular set of one or more photovoltaic panels and/or electronicmodules. The “pairing” between power generation components is typicallyperformed via initial assignment of codes and storage within each powergeneration component. The “pairing” process may take place at the timeof manufacture of power generation system components, duringinstallation of a power generation system, during the operation of thepower generation system and/or after an upgrade/modification to thepower generation system. The storage of codes typically establishes theelectrical connections and future communication protocols of signaling.

Referring now to the drawings, reference is now made to FIG. 1a whichshows a power generation circuit 101 according to an embodiment of thepresent invention. Two photovoltaic strings 120, by way of example, areconnected in parallel to an inverter 150. Details of only one of strings120 are shown explicitly. In each of strings 120, direct current powersources 116 are serially connected. Each direct current power source 116includes a photovoltaic panel 100 connected to an electronic module orphotovoltaic module 102. Outputs of photovoltaic modules 102 areconnected in series to form serial string 120. Photovoltaic modules 102may be direct current (DC) to DC converters such as a buck circuit,boost circuit, buck/boost or buck+boost circuit or any other knownswitching converter topology Attached to photovoltaic modules 102 is aprocessor 132 which accesses a memory 130. A transceiver 108 is attachedto the output of electronic module 102 and to processor 132. Accordingto a feature of the present invention, one of photovoltaic modules 102referenced 102 a is a master electronic module 102 a of string 120 andcontrols and communicates with the other modules, i.e. slave modules 102via power line communications or wireless link.

Load 150 is typically a direct current (DC) to alternating current (AC)inverter. String 120 attaches across the input of load 150. The outputof load 150 is typically attached to an AC grid voltage. Attached toload 150 is inverter module 104. Inverter module 104 contains a memorymodule 110, transceiver 118 and control unit 112. Inverter module 104 isattached to load 150 with bi-directional connection 114. Transducer 106is attached to the power connection to load 150 and provides a signal toinverter module 104.

Reference is now made to FIG. 2 which shows a method 201 according to anembodiment of the present invention. Method 201 mitigates thedetrimental effects of crosstalk in the communication channel along thepower lines connecting photovoltaic modules 102 with inverter module104. Method 201 illustrates two modes of operation, the first mode ofoperation is an initial mode 300 and the second mode of operation is anormal mode 500 during which there is normal conversion of power.

At the beginning of initial mode 300, current limiting (step 400)typically limits the DC current output of each electronic module 102.The limited DC current output of each module 102, prevents for example,the situation where the entire load 150 current (I_(L)) is beingsupplied by a single string 120 or some strings are not providing any ofthe load current (I_(L)).

An initial code stored in memory 110 modulates (step 202) a variation ofvoltage or current on the input of load 150 to produce an initialsignal. The initial signal is transmitted (step 203) from invertermodule 104. Direct electrical variation of current on the input of load150 may be achieved by using control line 114 to vary the inputimpedance of load 150 according to a code previously stored in memory110. The frequency of the transmitted control signal may be between 1 Hzand 100 Hz or may also be at higher frequencies.

The initial signal transmitted (step 203) from inverter module 104 isthen received (step 205) by electronic module 102. The initial signal issensed and a measure of the signal strength of the initial signal may beperformed. The measure of the signal strength of the initial signal maybe stored in memory 130. The initial signal is demodulated and/ordecoded (step 206) by transceiver 108 and the initial code correspondingto inverter module 104 is obtained from the demodulated output voltage.The initial code corresponding to inverter module 104 is stored (step207) in memory 130.

In order to end initial mode of operation in decision box 209, a controlsignal is typically modulated (step 210) and transmitted (step 211) frominverter module 104. The control signal is received (step 213) anddemodulated and/or decoded (step 214) by photovoltaic module 102 and acontrol code is stored. In decision box 215, the control code iscompared with the initial code and if the comparison is positive, i.e.the control code is the same as the initial code, then electronic module102 validates the command as coming from inverter module 104 with whichphotovoltaic module 102 is paired and not a control signal as crosstalkfrom another inverter module in the same photovoltaic generation field.In decision box 215, if the initial code positively compares with thecontrol code normal conversion of power (step 502) commences.

As an example, of a control signal is a keep alive signal 550. When keepalive signal is encoded with a valid control code then photovoltaicmodule 102 maintains normal conversion of power. Otherwise, if keepalive signal 550 is not encoded with a valid control signal, such as ifthe signal received is “pick-up” or cross talk from another inverter inthe photovoltaic field then in decision box 215 keep alive signal 550 isnot validated and photovoltaic module 102 enters initial mode 400 whichis typically a safety or current limited mode of operation until a validkeep alive signal 550 signal is received to enter normal operation 500.

There may be multiple possible frequencies for communication, and duringpairing (initial mode 300) the initial signal transmitted to andreceived by photovoltaic module 102 may specify to photovoltaic module102 which frequencies to listen to and to transmit on.

Signal strength may be also be used alternatively or in addition toinvalidate a control signal or at least set an alert condition.Typically, signal strength variation as measured by photovoltaic module102 from a transmission from inverter module 104 is not expected to varymore than a threshold ±3 decibel (dB). A variation of signal strengthmore between the initial transmission (step 203) and the controltransmission (step 211) greater than the threshold may set an alarmcondition or be used alternatively or in addition to invalidate acontrol signal in decision box 215 as being sourced by an unpairedinverter module 104.

Reference is now also made to FIG. 1b which illustrates schematicallyfurther details of power source 116, according to an embodiment of thepresent invention. The DC output of power source 116 is connected to acharge storage device 300 a. Charge storage device 300 a has a directcurrent (DC) output which supplies power to a modulator/demodulator unit302 a. A transducer/sensor 1106 attached to the output of module 102connects to modulator/demodulator 302 a. Modulator/demodulator unit 302a has a bi-directional connection to memory 130 and/or processor 132 forstoring a (de)modulation voltage V_(m) or a code decoded from an inputsignal. The DC output of charge storage device 300 a may provideprocessor 132 and memory 130 with DC power. Charge storage device 300 ais typically a battery or a capacitor which is charged via the DC outputof module 102 during daytime operation of power circuit 101. The chargestored in storage device 300 a during daytime may be used at nighttime.

Reference is now made FIG. 1e which shows further details of invertermodule 104 attached to load 150 in power generation circuit 101according to an embodiment of the present invention. The output of load150 is connected to an AC grid voltage. The AC grid voltage is connectedto charge storage device 300 b. Charge storage device 300 b is typicallya battery or a capacitor which is charged via the rectified grid voltageon the output of load 150 and/or from the DC input to load 150 duringdaytime operation.

Charge storage device 300 b has a direct current (DC) output whichsupplies power to modulator/demodulator unit 302 b. Transducer 106,connected at the input of load 150, is connected tomodulator/demodulator unit 302 b. Modulator/demodulator unit 302 b alsohas a connection to memory 110 or control unit 112. Control unit 112 isattached to memory 110. Control unit 112 is attached to load 150 viacontrol line 114. The DC output of charge storage device 300 b mayprovide control unit 112 and memory 110 with DC power.

Reference is now made to FIG. 1c which shows a method 103 used tooperate transceiver 108/118 according to different aspects of thepresent invention.

The transmission of the control signal from inverter module 104 ispreferably performed by transceiver 118 with method 103. Thetransmission of telemetries by photovoltaic module 102 is by transceiver108 with method 103. When photovoltaic module 102 sends telemetries, asource identification code identifying the photovoltaic module 102 asthe source and a destination identification code identifying invertermodule 104 as the destination may be included in the communicationsignal.

When transceiver 108/118 is operating as a transmitter, modulator 302 a/302 b causes a modulated signal to be superimposed (step 107) on to theDC power line. Modulator 302 a/ 302 b has an input voltage (V_(m)) whichcauses a current (I_(m)) to be drawn (step 105) from charge storagedevice 300 a/ 300 b which in turn draws current from the output ofmodule 102 and from the input of load 150 respectively. The currentdrawn from charge storage device 300 a/ 300 b is therefore a function ofthe input voltage i.e. modulating voltage (V_(m)). The superposition(step 107) of the modulated signal on to the DC power line is preferablyvia transducer 106/1106 or by a direct electrical connection (i.e. via acoupling capacitor) to the DC power line.

According to an exemplary embodiment of the present invention, thetransmission of the control signal from inverter module 104 isoptionally performed without the use of transducer 106. Instead themodulated control signal is made by altering of the input impedance ofload 150 according to a code in memory 110 via control line 114. Thevariation of the input impedance of load 150 causes the DC input currentof load 150 (drawn from modules 102) to vary by virtue of Ohm's law. Thedrawn current from modules 102 is sensed by transducer 1106 andde-modulated by transceiver 108 in module 102.

Reference is now made to FIG. 1d which shows a method 109 used tooperate transceiver 108/118 according to an aspect of the presentinvention. The reception of telemetries by inverter module 104 isperformed by transceiver 118 with method 109.

The reception of the control signal from inverter module 104 byphotovoltaic modules 102 is performed by transceiver 108 with method109. When transceiver 108/118 is operating as a receiver a signalpresent on the DC power line is extracted (step 111) from the DC powerline via transducer 106/1106 or by direct electrical connection (i.e.via coupling capacitor). Demodulator 302 a/ 302 b de-modulates thesensed signal present on the DC power line. In demodulation, the signalsensed and extracted (step 111) from the DC power line may vary (step113) the current (I_(m)) drawn from charge storage device 300 a/ 300 bwhich in turn draws current from the output of module 102 and from theinput of load 150 respectively to produce a demodulated output voltageV_(m). The demodulated output voltage (V_(m)) is a function of drawncurrent I_(m).

While the invention has been described with respect to a limited numberof embodiments, it will be appreciated that many variations,modifications and other applications of the invention may be made.

1-16. (canceled)
 17. A method for transmitting data via direct currentlines for energy transmission from a first communication unit to asecond communication unit, comprising: generating a high-frequencysignal having a predefined voltage amplitude by the second communicationunit and coupling the generated high-frequency signal onto the directcurrent lines using the second communication unit; sensing a currentlevel caused by the high-frequency signal on the direct current lines bythe first communication unit; determining a voltage amplitude for ahigh-frequency data signal based on the sensed current level caused bythe high-frequency signal using the first communication unit; andcoupling the high-frequency data signal having the determined voltageamplitude onto the direct current lines by the first communication unitfor the purpose of transmitting data to the second communication unit.18. The method of claim 17, wherein the high-frequency signal isrepeatedly coupled onto the direct current lines by the secondcommunication unit.
 19. The method of claim 18, wherein thehigh-frequency signal is coupled onto the direct current lines in acyclically repeated manner.
 20. The method of claim 17, wherein thehigh-frequency signal is coupled onto the direct current lines based ona predefined voltage amplitude.
 21. The method of claim 17, wherein thepredefined voltage amplitude is varied by the second communication unitwhich transmits the high-frequency signal.
 22. The method of claim 17,wherein the high-frequency signal is transmitted with encodedinformation, the encoded information comprising an identifier of thesecond communication unit which transmits the high-frequency signal. 23.The method of claim 17, wherein determining the voltage amplitude forthe high frequency data signal for transmitting the data comprisescalculating an impedance of a transmission path for the high-frequencysignal on the direct current lines from the sensed current level causedh the high-frequency signal and the voltage amplitude of thehigh-frequency signal.
 24. The method of claim 17, wherein the firstcommunication unit is assigned to and is local to a string ofphotovoltaic modules, and wherein the second communication unit isassigned to and is local to an inverter.
 25. The method of claim 17,wherein the first communication unit is assigned to and is local to aninverter, and wherein the second communication unit is assigned to andis local to a string of photovoltaic modules.
 26. A system fortransmitting data via direct current lines for energy transmission,comprising at least one first communication unit and at least one secondcommunication unit, each of the at least one first communication unitand the second communication unit comprising: a coupling-in circuitryconfigured to couple high-frequency signals onto the direct currentlines; and/or a coupling-out circuitry configured to couplehigh-frequency signals from the direct current lines, wherein the atleast one first communication unit or the at least one secondcommunication unit comprises an initial signal generator configured togenerate a high-frequency initial signal having a predefined voltageamplitude, the at least one first communication unit comprising: currentmeasuring circuitry configured to determine a current level caused bythe high-frequency initial signal on the direct current lines; a signalgenerator configured to generate a high-frequency data signal having avariable voltage amplitude for transmitting data to the at least onesecond communication unit: and a control device configured to set avoltage amplitude of the high-frequency data signal based on the currentlevel caused by the high-frequency initial signal.
 27. The system ofclaim 26, wherein the coupling-in circuitry and/or the coupling-outcircuitry of the at least one first communication unit and the at leastone second communication unit comprise a transducer.
 28. The system ofclaim 26, arranged in a photovoltaic (PV) installation having a PVgenerator comprising at least one string which is connected to aninverter via the direct current lines, and at least one of the at leastone first communication unit or the at least one second communicationunit respectively being assigned to the inverter and the at least onestring.
 29. The system of claim 28, wherein the PV installationcomprises at least two strings connected in parallel, and wherein thefirst communication unit or the second communication unit is assigned toat least one of the strings.
 30. A method for transmitting data viadirect current lines for energy transmission from a first communicationunit to a second communication unit, comprising: generating ahigh-frequency signal having a predefined voltage amplitude by thesecond communication unit and coupling the generated high-frequencysignal onto the direct current lines; sensing a current level caused bythe high-frequency signal on the direct current lines by the firstcommunication unit; determining a voltage amplitude for a high-frequencydata signal based on the sensed current level caused by thehigh-frequency signal by the first communication unit; and coupling thehigh-frequency data signal having the determined voltage amplitude ontothe direct current lines by the first communication unit for the purposeof transmitting data to the second communication unit.
 31. The method ofclaim 30, wherein the first communication unit is assigned to and islocal to a string of photovoltaic modules, and wherein the secondcommunication unit is assigned to and is local to an inverter.
 32. Themethod of claim 30, wherein the first communication unit is assigned toand is local to an inverter, and wherein the second communication unitis assigned to and is local to a string of photovoltaic modules.
 33. Themethod of claim 30, wherein the high-frequency signal is repeatedlycoupled onto the direct current lines by the second communication unit.34. The method of claim 30, wherein the high-frequency signal is coupledonto the direct current lines based on a predefined voltage amplitude.35. The method of claim 30, wherein the predefined voltage amplitude isvaried by the second communication unit which transmits thehigh-frequency signal.
 36. A method for transmitting data via directcurrent lines from a first module to a second module, comprising:generating, by the second module, a high-frequency control signal havinga predefined voltage amplitude and coupling the generated high-frequencycontrol signal onto the direct current lines using the second module;sensing, by the first module, a level of a current on the direct currentlines caused by the high-frequency control signal on the direct currentlines by the first module; determining, using the first module, avoltage amplitude for a high-frequency data signal based on the sensedlevel of the current caused by the high-frequency control signal; andcoupling, by the first module, the high-frequency data signal having thedetermined voltage amplitude onto the direct current lines fortransmission of data to the second module.
 37. The method of claim 36,wherein the high-frequency control signal is repeatedly coupled onto thedirect current lines by the second module.
 38. The method of claim 37,wherein the high-frequency control signal is coupled onto the directcurrent lines in a cyclically repeated manner.
 39. The method of claim36, wherein the high-frequency control signal is coupled onto the directcurrent lines based on a predefined voltage amplitude.
 40. The method ofclaim 36, wherein the second module modulates a variation of a voltageamplitude to transmit the high-frequency control signal.
 41. The methodof claim 36, wherein the high-frequency control signal is transmittedwith encoded information, the encoded information comprising anidentifier of the second module which transmits the high-frequencycontrol signal.
 42. The method of claim 36, wherein determining thevoltage amplitude for the high-frequency data signal for transmittingthe data comprises detecting a variation of impedance on the directcurrent lines from the high frequency control signal.
 43. The method ofclaim 36, wherein the first module is assigned to and is local to astring of photovoltaic modules, and wherein the second module isassigned to and is local to an inverter.
 44. The method of claim 36,wherein the first module is assigned to and is local to an inverter, andwherein the second module is assigned to and is local to a string ofphotovoltaic modules.
 45. A system for transmitting data via directcurrent lines comprising: at least one first communication module; andat least one second communication module, wherein each of the at leastone first communication module and the second communication modulecomprising: a coupling-in circuitry configured to couple high-frequencysignals onto the direct current lines; and/or a coupling-out circuitryconfigured to couple high-frequency signals from the direct currentlines, and wherein the at least one first communication module or the atleast one second communication module comprises signal generatorconfigured to generate a high-frequency signal having a predefinedvoltage amplitude, the at least one first communication modulecomprising: current sensing circuitry configured to determine a currentlevel caused by the high-frequency signal on the direct current lines; asignal generator circuit configured to generate a high-frequency datasignal for transmitting data to the at least one second communicationmodule; and a control device configured to set a voltage amplitude ofthe high-frequency data signal based on the determined current levelcaused by the high-frequency signal.
 46. The system of claim 45, whereinthe coupling-in circuitry and/or the coupling-out circuitry of the atleast one first communication module and the at least one secondcommunication module comprise a transducer.
 47. The system of claim 45,arranged in a photovoltaic (PV) installation comprising at least onestring which is connected to an inverter via the direct current lines,and at least one of the at least one first communication module or theat least one second communication module respectively being assigned tothe inverter and the at least one string.
 48. The system of claim 47,wherein the PV installation comprises at least two strings connected inparallel, and wherein the first communication module or the secondcommunication module is assigned to at least one of the at least twostrings.
 49. A method for transmitting data via direct current lines forenergy transmission from a first communication module to a secondcommunication module, comprising: generating, by the secondcommunication module, a high-frequency signal having a predefinedvoltage amplitude coupling the generated high-frequency signal onto thedirect current lines; sensing a level of a current on the direct currentlines caused by the high-frequency signal; determining a voltageamplitude for a data signal based on the sensed current level caused bythe high-frequency signal; and coupling, by the first communicationmodule, the high-frequency data signal having the determined voltageamplitude onto the direct current lines, the high-frequency data signalconfigured to transmit data to the second communication module.
 50. Themethod of claim 49, wherein the first communication module is assignedto and is local to a string of photovoltaic modules, and wherein thesecond communication module is assigned to and is local to an inverter.51. The method of claim 49, wherein the first communication module isassigned to and is local to an inverter, and wherein the secondcommunication module is assigned to and is local to a string ofphotovoltaic modules.
 52. The method of claim 49, wherein thehigh-frequency signal is repeatedly coupled onto the direct currentlines by the second communication module.
 53. The method of claim 49,wherein the high-frequency signal is coupled onto the direct currentlines based on a predefined voltage amplitude.
 54. The method of claim49, wherein the second communication module modulates a variation of avoltage amplitude to transmit the high-frequency signal.
 55. A methodfor transmitting data via direct current lines in a photovoltaic powergeneration system, the method comprising: generating, by a secondcommunication module, a control signal having a predefined voltageamplitude and coupling the generated control signal onto the directcurrent lines using the second communication module; sensing, by asensor of a first communication module, a current level on the directcurrent lines caused by the control signal; determining, by the firstcommunication module, a voltage amplitude for a data signal based on thesensed current level caused by the control signal; and coupling, by thefirst communication module, the data signal with the determined voltageamplitude onto the direct current lines, the data signal configured totransmit telemetry data to the second communication module.
 56. Themethod of claim 55, wherein the control signal is repeatedly coupledonto the direct current lines by the second communication module. 57.The method of claim 56, wherein the control signal is a keep alivesignal repeatedly coupled onto the direct current lines.
 58. The methodof claim 55, wherein the control signal is coupled onto the directcurrent lines based on a predefined voltage amplitude.
 59. The method ofclaim 55, wherein the second communication module modulates a variationof a voltage amplitude to transmits the control signal.
 60. The methodof claim 55, wherein the control signal is transmitted with encodedinformation, the encoded information comprising an identifier of thesecond communication module which transmits the control signal.
 61. Themethod of claim 55, wherein determining the voltage amplitude for thedata signal for transmitting the telemetry data comprises detecting avariation of impedance on the direct current lines caused by the controlsignal.
 62. The method of claim 55, wherein the first communicationmodule is associated with and connected to a string of photovoltaicmodules, and wherein the second communication module is associated withand connected to an inverter.
 63. The method of claim 55, wherein thecontrol signal is a high-frequency signal and the data signal is ahigh-frequency signal.
 64. A system for transmitting data via directcurrent lines in a photovoltaic (PV) installation, the systemcomprising: at least one first communication unit; and at least onesecond communication unit, wherein each of the at least one firstcommunication unit and the second communication unit comprises: a signalcoupling circuitry configured to couple communication signals onto andfrom the direct current lines; and wherein the at least one firstcommunication unit further comprises: an initial signal generatorconfigured to generate an initial signal having a predefined voltageamplitude; and wherein the at least one second communication unitcomprises: current measuring circuitry configured to determine a currentlevel caused by the initial signal on the direct current lines; a datasignal generator configured to generate a data signal having anadjustable voltage amplitude for transmitting data to the at least onefirst communication unit; and a control device configured to set avoltage amplitude of the data signal based on the determined currentlevel caused by the initial signal on the direct current lines.
 65. Thesystem of claim 64, wherein the signal coupling circuitry of the atleast one first communication unit and the at least one secondcommunication unit comprises a coupling capacitor unit.
 66. The systemof claim 64, further comprising: a PV generator comprising at least onePV string which is connected to an inverter via the direct currentlines, wherein at least one of the at least one first communication unitor the at least one second communication unit respectively beingassociated with the inverter and the at least one string.
 67. The systemof claim 66, wherein the PV generator comprises at least two stringsconnected in parallel, and wherein the first communication unit or thesecond communication unit is associated with at least one of the atleast two strings.
 68. A method for transmitting data via direct currentlines from a first communication unit to a second communication unit,comprising: generating, by the second communication unit, a controlsignal having a predefined voltage amplitude and coupling the generatedcontrol signal onto the direct current lines; sensing, by the firstcommunication unit, a current level on the direct current lines causedby the control signal; determining, by the first communication unit, avoltage amplitude for a data signal based on the sensed current levelcaused by the control signal on the direct current lines; andgenerating, by the first communication unit, the data signal having thedetermined voltage amplitude and coupling the data signal onto thedirect current lines to transmit data to the second communication unit.69. The method of claim 68, wherein the first communication unit isassociated with and connected to a string of photovoltaic modules, andwherein the second communication unit is associated with and connectedto an inverter.
 70. The method of claim 68, wherein the control signalis a high-frequency signal and the data signal is a high-frequencysignal.
 71. The method of claim 68, wherein the control signal isrepeatedly coupled onto the direct current lines by the secondcommunication unit.
 72. The method of claim 68, wherein the controlsignal is coupled onto the direct current lines based on a storedvoltage amplitude.
 73. The method of claim 68, wherein the secondcommunication unit modulates a variation of a voltage amplitude totransmit the control signal.
 74. A system for transmitting data viadirect current lines of a photovoltaic power generator, the systemcomprising: a first communication module associated with an inverter,the first communication module comprising: a first signal generatorconfigured to generate a control signal having a predefined voltageamplitude; and a first coupling circuitry for coupling the controlsignal onto a direct current line to transmit the control signal on thedirect current line; and a second communication module associated with astring of photovoltaic modules, the second communication modulecomprising: a current sensor for detecting a current level on the directcurrent lines caused by the control signal; a control device configuredto determine a voltage amplitude of a data signal, wherein the voltageamplitude of the data signal is based on the detected current level; asecond signal generator configured to generate the data signal with thedetermined voltage amplitude; and a second coupling circuitry forcoupling the data signal onto a direct current line to transmit the datasignal to the first communication module.
 75. The system of claim 74wherein the control signal is a high-frequency control signal and thedata signal is a high-frequency data signal.
 76. A method fortransmitting data via direct current lines of a power generator system,the method comprising: modulating, by a first communication module, acontrol signal with a predefined voltage amplitude; transmitting, by afirst communication module and to a second communication module, thecontrol signal via the direct current lines by coupling the controlsignal onto the direct current lines; demodulating, by a secondcommunication module, the control signal to determine a current level ofthe direct current lines caused by the coupling of the control signalonto the direct current lines; determining, by the second communicationmodule, a voltage amplitude of a data signal to be coupled on the directcurrent lines, wherein the voltage amplitude is based on the determinedcurrent level caused by the coupling of the control signal onto thedirect current lines; modulating, by the second communication module,the data signal with the determined voltage amplitude; and coupling, bythe second communication module, the data signal onto the direct currentlines for transmission of data to the first communication module. 77.The method of claim 76 wherein the control signal is a high-frequencycontrol signal and the data signal is a high-frequency data signal. 78.A method for transmitting data in a photovoltaic power generator system,the method comprising: generating, by a first modulator of a firstcommunication unit associated with an inverter, a control signal havinga predefined voltage amplitude; coupling, by a first transducer of thefirst communication unit, the generated control signal onto a directcurrent line of the photovoltaic power generator system; sensing, by asecond transducer of a second communication unit associated with atleast one photovoltaic module of the photovoltaic power generatorsystem, a current level caused by the control signal on the directcurrent line; demodulating, by a second modulator of the secondcommunication unit, the control signal to determine a voltage amplitudefor a data signal to be transmitted to the first communication unit,wherein the voltage amplitude of the data signal is based on the sensedcurrent level caused by the control signal on the direct current line;and coupling, by the second transducer of the second communication unit,the data signal having the determined voltage amplitude onto the directcurrent line to transmit data to the first communication unit.
 79. Themethod of claim 78 wherein the control signal is a high-frequencycontrol signal and the data signal is a high-frequency data signal. 80.The method of claim 17 wherein the high-frequency signal having thepredefined voltage amplitude is generated by a modulator/demodulatorunit connected to a storage device storing the predefined voltageamplitude, the high-frequency signal causing a charge to be drawn fromthe storage device connected to the modulator/demodulator unit.
 81. Themethod of claim 17 wherein the data transmitted on the high-frequencydata signal comprises: telemetries associated with a photovoltaicmodule; a source identification code identifying the first communicationunit; and destination identification code identifying the secondcommunication unit.
 82. The method of claim 80 further comprising:comparing a control code associated with the high-frequency signal to aninitial code stored in the storage device; and validating, based on thecomparison, a received control command as originating from the secondcommunication unit.
 83. The system of claim 26 wherein the signalgenerator comprises: a modulator/demodulator unit connected to a storagedevice storing the predefined voltage amplitude, wherein thehigh-frequency data signal causes a charge to be drawn from the storagedevice connected to the modulator demodulator unit.
 84. The system ofclaim 26 wherein the data transmitted on the high-frequency data signalcomprises: telemetries associated with a photovoltaic module; a sourceidentification code identifying the first communication unit; and adestination identification code identifying the second communicationunit.
 85. The system of claim 26 wherein the current measuring circuitrycomprises: a transducer connected to a modulator/demodulator unit; acharge storage device connected to the modulator/demodulator unit; and amemory for storing the voltage amplitude of the high-frequency datasignal.
 86. The method of claim 30 wherein the high-frequency signalhaving the predefined voltage amplitude is generated by amodulator/demodulator unit connected to a storage device storing thepredefined voltage amplitude, the high-frequency signal causing a chargeto be drawn from the storage device connected to themodulator/demodulator unit.
 87. The method of claim 30 wherein the datatransmitted on the high-frequency data signal comprises: telemetriesassociated with a photovoltaic module; a source identification codeidentifying the first communication unit; and a destinationidentification code identifying the second communication unit.
 88. Themethod of claim 86 further comprising: comparing a control codeassociated with the high-frequency signal to an initial code stored inthe storage device; and validating, based on the comparison, a receivedcontrol command as originating from the second communication unit. 89.The method of claim 36 wherein the high-frequency control signal havingthe predefined voltage amplitude is generated by a modulator/demodulatorunit connected to a storage device storing the predefined voltageamplitude, the high-frequency control signal causing a charge to bedrawn from the storage device connected to the modulator/demodulatorunit.
 90. The method of claim 36 wherein the data transmitted on thehigh-frequency data signal comprises: telemetries associated with aphotovoltaic module; a source identification code identifying the firstmodule; and a destination identification code identifying the secondmodule.
 91. The method of claim 89 further comprising: comparing acontrol code associated with the high-frequency control signal to aninitial code stored in the storage device; and validating, based on thecomparison, a received control command as originating from the secondmodule.
 92. The system of claim 45 wherein the signal generator circuitcomprises: a modulator/demodulator unit connected to a storage devicestoring the predefined voltage amplitude, wherein the high-frequencydata signal causes a charge to be drawn from the storage deviceconnected to the modulator/demodulator unit.
 93. The system of claim 45wherein the data transmitted on the high-frequency data signalcomprises: telemetries associated with a photovoltaic module; a sourceidentification code identifying the first communication module; and adestination identification code identifying the second communicationmodule.
 94. The system of claim 45 wherein the current sensing circuitrycomprises: a transducer connected to a modulator/demodulator unit; acharge storage device connected to the modulator/demodulator unit; and amemory for storing the voltage amplitude of the high-frequency datasignal.
 95. The method of claim 49 wherein the high-frequency signalhaving the predefined voltage amplitude is generated by amodulator/demodulator unit connected to a storage device storing thepredefined voltage amplitude, the high-frequency signal causing a chargeto be drawn from the storage device connected to themodulator/demodulator unit.
 96. The method of claim 49 wherein the datatransmitted on the high-frequency data signal comprises: telemetriesassociated with a photovoltaic module; a source identification codeidentifying the first communication module; and a destinationidentification code identifying the second communication module.
 97. Themethod of claim 95 further comprising: comparing a control codeassociated with the high-frequency signal to an initial code stored inthe storage device; and validating, based on the comparison, a receivedcontrol command as originating from the second communication module. 98.The method of claim 55 wherein the control signal having the predefinedvoltage amplitude is generated by a modulator/demodulator unit connectedto a storage device storing the predefined voltage amplitude, thecontrol signal causing a charge to be drawn from the storage deviceconnected to the modulator/demodulator unit.
 99. The method of claim 55wherein the telemetry data transmitted on the data signal comprises:telemetries associated with a photovoltaic module; a sourceidentification code identifying the first communication module; and adestination identification code identifying the second communicationmodule.
 100. The method of claim 98 further comprising: comparing acontrol code associated with the control signal to an initial codestored in the storage device; and validating, based on the comparison, areceived control command as originating from the second communicationmodule.
 101. The system of claim 64 wherein the data signal generatorcomprises: a modulator/demodulator unit connected to a storage devicestoring the predefined voltage amplitude, wherein the data signal causesa charge to be drawn from the storage device connected to themodulator/demodulator unit.
 102. The system of claim 64 wherein the datatransmitted on the data signal comprises: telemetries associated with aphotovoltaic module; a source identification code identifying the firstcommunication unit; and a destination identification code identifyingthe second communication unit.
 103. The system of claim 64 wherein thecurrent measuring circuitry comprises: a transducer connected to amodulator/demodulator unit; a charge storage device connected to themodulator/demodulator unit; and a memory for storing the voltageamplitude of the data signal.
 104. The method of claim 68 wherein thecontrol signal having the predefined voltage amplitude is generated by amodulator/demodulator unit connected to a storage device storing thepredefined voltage amplitude, the control signal causing a charge to bedrawn from the storage device connected to the modulator/demodulatorunit.
 105. The method of claim 68 wherein the data transmitted on thedata signal comprises: telemetries associated with a photovoltaicmodule; a source identification code identifying the first communicationunit; and a destination identification code identifying the secondcommunication unit.
 106. The method of claim 104 further comprising:comparing a control code associated with the control signal to aninitial code stored in the storage device; and validating, based on thecomparison, a received control command as originating from the secondcommunication unit.